The present invention relates to a tap for a gas, liquefied gas, or other fluid vessel, comprising a tap body having a main body portion and a base end portion provided with a first external thread for securing the tap to a neck opening of the vessel, and particularly to a tap having a clamping ring adapted to be firmly screwed down against a radial surface of the vessel neck surrounding the neck opening. The invention also concerns a method for securing a tap to a gas or fluid vessel, as well as a gas or fluid vessel having a tap of the type referred to.
In the state of the art the tap of a gas vessel is normally provided with a base end portion having an external conical thread engaged by application of a predetermined torque into a threaded opening of a gas vessel. The conical thread provides a tight connection between the base end portion of the tap and the vessel. If a high lateral or axial impact force is exerted to the tap, the base end portion may be deformed causing leakage through the threaded engagement between the base end portion and the opening of the vessel neck. Such leakage must be avoided especially for highly oxidant, reactive, corrosive, or toxic gases, used for example in the fabrication of microchips in the semiconductor industry. The known taps for gas vessels are usually provided with a single primary valve (single external closure) disposed within the tap body exteriorly of the gas vessel. If a high impact force is exerted to this known tap, for example in case of an accident of a vehicle wherein the vessel is transported, the portion of the tap body containing a primary valve may be sheared off and the gas may flow out freely through the gas passage of the base end portion which remains engaged in the vessel neck and, possibly also between the threads of the base end portion and the vessel neck, as referred to above.
It has already been proposed to provide a check valve below the base end portion and which is thus located within the interior of the vessel when the tap is secured thereto. This check valve may be a non-active check valve which closes only under the effect of the pressure of the fluid contained within the vessel in case the main portion of the tap body is sheared off. Also known are active check valves which close prior to each closure of the primary valve and which are positively opened after each opening of the primary valve. The taps provided with such a check valve and a primary valve are taps of double, internal and external, closures comprising the primary valve exteriorly of the vessel and the check valve interiorly thereof. Unfortunately these check valves can only prevent leakage of the contents of the vessel through the normal flow passage of the base end portion of the tap body remaining engaged within the opening of the vessel neck after the main portion of the tap body has been sheared off, but these check valves cannot prevent leakage through the engaged threads of the base end portion and the vessel neck in case of deformation of the base portion caused by the strong impact force applied to the tap.
Known in the prior art, such as French patent 2,602,303, is a seal ring disposed about the base end portion of the valve body and having O-rings engaging the fluid vessel and the tap body to provide an additional sealing means, but this seal ring cannot prevent damaging of the threaded engagement between the tap body and the vessel in case of application of a strong impact force applied to the tap.